The present invention relates to an electric discharge machine for generating electric discharges in a working gap formed between a tool electrode and a workpiece while supplying dielectric fluid to the working gap. More particularly, the present invention relates to a work tank for storing dielectric fluid in which a workpiece has been immersed, or gathering dielectric fluid which, after being jetted at the working gap, is scattered away.
Generally, a workpiece is positioned inside a work tank, and the work tank is filled with dielectric fluid such as kerosene or water with high electrical resistivity. A tool electrode is positioned extremely close to the workpiece. When a power pulse is applied across the workpiece and the tool electrode, the insulation characteristics of the dielectric fluid in the work gap are broken down and an electric discharge is produced. Microscopic amounts of the workpiece material are evaporated or molten by the heat caused by this electric discharge, and washed into the dielectric fluid. In order to restore the insulation characteristics of the dielectric in the working gap, application of the power pulse is stopped for a fixed time. During electric discharge machining, the breakdown and restoration of the insulation characteristics of the dielectric fluid is repeated cyclically. In addition to its function as an insulator, the dielectric fluid also functions to wash away scraps of the workpiece material, and to cool the working gap. Electric discharge machining methods have been used in which dielectric fluid is jetted into the work gap using an appropriate nozzle without storing the dielectric fluid in a work tank. With this type of electric discharge machining method, in order to save dielectric fluid, a work tank enclosing the workpiece is used to catch and gather any dielectric fluid which scatters from the working gap.
At least the front part of the work tank is movable so that in preparation for machining an operator can easily get close to the workpiece or tool electrode inside the work tank. For example, a work tank having a front door which is hinged on one side and can turn horizontally, is known. This type of work tank requires a large space when opening the front door. Japanese Laid-open Patent 8-71850 discloses a work tank having a front door capable of being folded in half from top to bottom. The work tank disclosed in this publication makes the space required to open the front door smaller.
An object of the present invention is to provide a work tank for an electric discharge machine that can rapidly perform continuous closing and locking of a front door.
Another object of the present invention is to provide a work tank for an electric discharge machine that can rapidly perform continuous unlocking and opening of a front door.
Yet another object of the present invention is to provide a work tank for an electric discharge machine that does not require a large space when opening a front door.
According to the present invention, a work tank for an electric discharge machine in which dielectric fluid is supplied between a workpiece and a tool electrode comprises
a tank wall having an opening on a front side and surrounding a workpiece,
a front door horizontally movable between an unlock position where the front door is vertically movable, and a lock position where the opening is closed in a generally liquid-tight relationship,
a pair of brackets attached to both sides of the front door and extending rearward,
a handle lever supported on at least one of the pair of brackets so as to pivot about the fulcrum,
a cam follower, fixed to the handle lever further forward than the fulcrum, and being vertically movable between a first position higher up than the fulcrum and a second position lower down than the fulcrum, and
a movement restricting member for restricting horizontal movement of the cam follower.
When the cam follower is at the first position, the front door is in the unlock position and is vertically movable. When the cam follower is at the second position, the front door is in the lock position and the opening is held closed in generally liquid-tight relationship.
Preferably, the handle levers are supported on each of the pair of brackets, and a handle is provided for connecting respective tips of the handle levers.
The movement restriction member is preferably a rail block having a vertically extending groove into which the cam follower is loosely fitted.
Preferably, a guide block, having a guide groove extending vertically and then extending rearward from the upper end, is attached to the tank wall, and a guide pin that can be fitted into the guide groove is provided on the bracket.
It is also preferable to provide stopper pins on the bracket, for restricting the pivoting angle of the handle lever by contacting the handle lever.
Other objects and novel features of the present invention will become clear upon reference to the following description.